Sulfonium

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Structure of (CH3)3S . The C-S-C angles are 102deg and C-S bond distance is 177 picometers. (CH3)3S+ in the BPh4- salt (code HEYZAM).png
Structure of (CH3)3S . The C-S-C angles are 102° and C-S bond distance is 177 picometers.

In organic chemistry, a sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively-charged ion (a "cation") featuring three organic substituents attached to sulfur. These organosulfur compounds have the formula [SR3]+. Together with a negatively-charged counterion, they give sulfonium salts. They are typically colorless solids that are soluble in polar organic solvent. [2] [3]

Contents

Synthesis

Dimethylsulfoniopropionate (DMSP), is found in marine phytoplankton and seaweeds. Dimethylsulfoniopropionate Structural Formula V1.svg
Dimethylsulfoniopropionate (DMSP), is found in marine phytoplankton and seaweeds.

Sulfonium compounds are usually synthesized by the reaction of thioethers with alkyl halides. For example, the reaction of dimethyl sulfide with iodomethane yields trimethylsulfonium iodide:

CH3SCH3 + CH3I → (CH3)3S+I−

The reaction proceeds by a nucleophilic substitution mechanism (SN2), where iodide is the leaving group. For weakly electrophilic alkyl halides, the reactions can be accelerated by the addition of silver tetrafluoroborate. In that vein, the rate (and irreversibility) of methylation improves with more electrophilic methylating agents such as methyl trifluoromethanesulfonate.

These S-alkylations can be reversible, especially when the leaving group is iodide. For example, alkylation of dimethylsulfide with allyl iodide gives trimethylsulfonium iodide. In a related process, secondary alkyl halides react with dimethylsulfide to give mixed thioether, eliminating methyl halide. [5]

Below are listed some other synthetic methods, among many: [5]

Inversion

Sulfonium ions with three different substituents are chiral owing to their pyramidal structure. Unlike the isoelectronic oxonium ions (R3O+), chiral sulfonium ions are resolvable into optically stable enantiomers. [6] [Me(Et)SCH2CO2H]+ is the first chiral sulfonium cation to be resolved into enantiomers. [7] The barrier to inversion ranges from 100 to 130 kJ/mol. [3]

Applications and occurrence

Biochemistry

The sulfonium (more specifically methioninium) species S-adenosylmethionine occurs widely in nature, where it is used as a source of the adenosoyl or methyl radicals. These radicals participate in the biosynthesis of many compounds. [8] [9]

Structure of S-adenosylmethionine. S-Adenosyl-L-methionin.svg
Structure of S-adenosylmethionine.

Other naturally-occurring sulfonium species are S-methylmethionine (methioninium) and the related dimethylsulfoniopropionate (DMSP).

Organic synthesis

Sulfonium salts are precursor to sulfur ylides, which are useful in carbon–carbon bond-forming reactions. In a typical application, a R2S+CH2R′ center is deprotonated to give the ylide R2S+CHR−. [10] These ylides add to ketones and aldehydes to give epoxides (Johnson–Corey–Chaykovsky reaction). [11]

Structure of tris(dimethylamino)sulfonium difluorotrimethylsilicate. TASF.png
Structure of tris(dimethylamino)sulfonium difluorotrimethylsilicate.

Tris(dimethylamino)sulfonium difluorotrimethylsilicate [((CH3)2N)3S]+[F2Si(CH3)3]− is a popular fluoridation agent. [12]

Some azo dyes are modified with sulfonium groups to give them a positive charge. The compound triphenylsulfonium triflate is a photoacid, a compound that under light converts to an acid.[ citation needed ]

Organic sulfides react with liquid bromine to give bromosulfonium bromides, i.e.: [13]

RSR′ + [RR′S+Br]Br−

See also

References

  1. ↑ Knop, Osvald; Cameron, T. Stanley; Bakshi, Pradip K.; Linden, Antony; Roe, Stephen P. (1994). "Crystal Chemistry of Tetraradial Species. Part 5. Interaction Between Cation Lone Pairs and Phenyl Groups in Tetraphenylborates: Crystal Structures of Me3S+, Et3S+, Me3SO+, Ph2I+, and 1-Azoniapropellane Tetraphenylborates". Canadian Journal of Chemistry. 72 (8): 1870–1881. doi:10.1139/v94-238.
  2. ↑ C. J. M. Stirling, ed. (1981). The Sulphonium Group: Part 1, Volume 1. PATAI'S Chemistry of Functional Groups. John Wiley & Sons. doi:10.1002/9780470771648. ISBN   9780470771648.C. J. M. Stirling, ed. (1981). The Sulphonium Group: Part 2, Volume 2. PATAI'S Chemistry of Functional Groups. John Wiley & Sons. doi:10.1002/9780470771655. ISBN   9780470771655.
  3. 1 2 Kozhushkov, Sergei I.; Alcarazo, Manuel (2020). "Synthetic Applications of Sulfonium Salts". European Journal of Inorganic Chemistry. 2020 (26): 2486–2500. doi:10.1002/ejic.202000249. PMC   7386937 . PMID   32742188.
  4. ↑ DeBose, Jennifer L.; Sean C. Lema; Gabrielle A. Nevitt (2008-03-07). "Dimethylsulfoniopropionate as a foraging cue for reef fishes". Science. 319 (5868): 1356. Bibcode:2008Sci...319.1356D. doi:10.1126/science.1151109. PMID   18323445. S2CID   20782786.
  5. 1 2 Lowe, P. A. (1981). "Synthesis of Sulphonium Salts". The Sulfonium Group: Vol. 1 (1981). PATAI's Chemistry of Functional Groups. pp. 267–312. doi:10.1002/9780470771648.ch11. ISBN   978-0-470-77164-8.
  6. ↑ March, J. "Advanced Organic Chemistry" 5th Ed. J. Wiley and Sons, 1992: New York. ISBN   0-471-60180-2
  7. ↑ Barbachyn, Michael R.; Johnson, Carl R. (1984). "Optical Activation and Utilization of Compounds Containing Chiral Sulfur Centers". Asymmetric Synthesis. pp. 227–261. doi:10.1016/B978-0-12-507704-0.50007-6. ISBN   9780125077040.
  8. ↑ Layer, G.; Heinz, D. W.; Jahn, D.; Schubert, W.-D. "Structure and function of radical SAM enzymes" Current Opinion in Chemical Biology 2004, volume 8, 468-476. doi : 10.1016/j.cbpa.2004.08.001
  9. ↑ Perry A. Frey, Olafur Th. Magnusson "S-Adenosylmethionine:  A Wolf in Sheep's Clothing, or a Rich Man's Adenosylcobalamin?" Chem. Rev., 2003, 103 (6), pp 2129–2148. doi : 10.1021/cr020422m
  10. ↑ Mitchell J. Bogdanowicz, Barry M. Trost (1974). "Cyclopropylphenylsulfonium Tetrafluoroborate". Organic Syntheses . 54: 27. doi:10.15227/orgsyn.054.0027 .
  11. ↑ Kaiser, Daniel; Klose, Immo; Oost, Rik; Neuhaus, James; Maulide, Nuno (2019). "Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts". Chemical Reviews. 119 (14): 8701–8780. doi:10.1021/acs.chemrev.9b00111. PMC   6661881 . PMID   31243998.
  12. ↑ W. J. Middleton (1986). "Tris(dimethylamino)sulfonium difluorotrimethylsilicate". Organic Syntheses . 64: 221. doi:10.15227/orgsyn.064.0221 .
  13. ↑ Magee, Philip S. (1971). "The Sulfur–Bromine Bond". In Senning, Alexander (ed.). Sulfur in Organic and Inorganic Chemistry. Vol. 1. New York: Marcel Dekker. pp. 316–321. ISBN   0-8247-1615-9. LCCN   70-154612.
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